Sampling networks are useful building blocks that find applications in many types of integrated circuits. Common uses for sampling networks include switched capacitor filters, sample and hold circuits, track and hold circuits, and others. When combined with an integrator, they can form an input stage for a sigma-delta modulator.
Sampling networks are efficiently implemented using MOSFET transistors. As a result, sampling networks have become much more popular with the increasing use of MOSFETs in analog and mixed signal applications.
In sigma-delta modulators, two signals are added together by sampling the signals and integrating the result. In one specific example, an analog signal being converted to a digital word is sampled and a reference voltage or signal that is the output of a one-bit digital-to-analog converter is subtracted from it.
The sampling of these signals can create voltages that exceed the supply voltage ranges of an integrated circuit on which these actives are performed. This in turn can lead to transient voltages that cause parasitic diodes to conduct and clamp voltages. This causes errors in the integrated output voltage.
Accordingly, what is needed are circuits, methods, and apparatus that provide sampling networks that avoid these undesirable transient voltages.